Polymers, resist compositions and patterning process

ABSTRACT

A copolymer of an acrylate monomer containing fluorine at α-position with a fluorinated hydroxystyrene derivative is highly transparent to VUV radiation and resistant to plasma etching. A resist composition using the polymer as a base resin is sensitive to high-energy radiation below 200 nm, has excellent sensitivity, resolution, transparency, substrate adhesion and plasma etching resistance, and is suited for lithographic microprocessing.

This invention relates to polymers useful as the base resin in resist compositions suited for microfabrication.

It also relates to resist compositions, especially chemical amplification resist compositions comprising the polymers, and a patterning process using the same.

BACKGROUND OF THE INVENTION

In the drive for higher integration and operating speeds in LSI devices, the pattern rule is made drastically finer. The rapid advance toward finer pattern rules is grounded on the development of a projection lens with an increased NA, a resist material with improved performance, and exposure light of a shorter wavelength. To the demand for a resist material with a higher resolution and sensitivity, chemical amplification positive working resist materials which are catalyzed by acids generated upon light exposure are effective as disclosed in U.S. Pat No. 4,491,628 and U.S. Pat. No. 5,310,619 (JP-B 2-27660 and JP-A 63-27829). They now become predominant resist materials especially adapted for deep UV lithography. Also, the change-over from i-line (365 nm) to shorter wavelength KrF laser (248 nm) brought about a significant innovation. Resist materials adapted for KrF excimer lasers enjoyed early use on the 0.3 micron process, passed through the 0.25 micron rule, and currently entered the mass production phase on the 0.18 micron rule. Engineers have started investigation on the 0.15 micron rule, with the trend toward a finer pattern rule being accelerated.

For ArF laser (193 nm), it is expected to enable miniaturization of the design rule to 0.13 μm or less. Since conventionally used novolac resins and polyvinylphenol resins have very strong absorption in proximity to 193 nm, they cannot be used as the base resin for resists. To ensure transparency and dry etching resistance, some engineers investigated acrylic and alicyclic (typically cycloolefin) resins as disclosed in JP-A 9-73173, JP-A 10-10739, JP-A 9-230595 and WO 97/33198.

With respect to F₂ excimer laser (157 nm) which is expected to enable further miniaturization to 0.10 μm or less, more difficulty arises in insuring transparency because it was found that acrylic resins which are used as the base resin for ArF are not transmissive to light at all and those cycloolefin resins having carbonyl bonds have strong absorption. It was also found that polyvinyl phenol) which is used as the base resin for KrF has a window for absorption in proximity to 160 nm, so the transmittance is somewhat improved, but far below the practical level.

SUMMARY OF THE INVENTION

An object of the invention is to provide a novel polymer having a high transmittance to vacuum ultraviolet radiation of up to 300 nm, especially F₂ (157 nm), Kr₂ (146 nm), KrAr (134 nm) and Ar₂ (121 nm) excimer laser beams, and useful as the base resin in a resist composition. Another object is to provide a resist composition, and especially a chemical amplification resist composition, comprising the polymer, and a patterning process using the same.

It has been found that using as the base polymer a copolymer of an acrylate monomer containing fluorine at α-position with a fluorinated hydroxystyrene derivative, a resist composition, especially a chemically amplified resist composition, having a drastically improved transparency, substrate adhesion, resolution and dry etching resistance is obtained.

In a first aspect, the invention provides a polymer comprising recurring units of the following general formulae (1a) and (1b) or (1a), (1b) and (1c) and having a weight average molecular weight of 1,000 to 500,000.

Herein R¹, R², R⁵ to R⁷ and R¹⁰ to R¹² each are hydrogen, a fluorine atom or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R³ is a fluorine atom or a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms; R⁴ and R⁸ each are hydrogen or an acid labile group; R⁹ and R¹⁴ each are a fluorine atom or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R¹³ is —C(CF₃)₂—O—R¹⁵; R¹⁵ is hydrogen or an acid labile group; a, b and c are numbers in the range: 0<a<1, 0<b<1, 0≦c<1, and 0<a+b+c≦1; d is an integer of 1 to 4; e and f each are an integer of 0 to 5, and 1≦e+f≦5.

In a preferred embodiment, R³ in formula (1a) is a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms, and most preferably trifluoromethyl.

In a second aspect, the invention provides a resist composition comprising the polymer defined above, and preferably a chemically amplified positive resist composition comprising (A) the polymer defined above, (B) an organic solvent, (C) a photoacid generator, and optionally, (D) a basic compound and/or (E) a dissolution inhibitor.

In a third aspect, the invention provides a process for forming a resist pattern comprising the steps of applying the resist composition onto a substrate to form a coating; heat treating the coating and then exposing it to high-energy radiation in a wavelength band of 100 to 180 nm or 1 to 30 nm through a photo mask; and optionally heat treating the exposed coating and developing it with a developer. The high-energy radiation is typically an F₂ laser beam, Ar₂ laser beam or soft x-ray.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Polymer

For improving the transmittance in proximity to 157 nm, reducing the number of carbonyl groups and/or carbon-to-carbon double bonds is contemplated to be one effective way. It was also found that introducing fluorine atoms into base polymers makes a great contribution to improved transmittance. The inventor has found that copolymers of an acrylate monomer containing fluorine at α-position, a fluorinated hydroxystyrene monomer and optionally, a fluorinated styrene monomer have a high transparency at a wavelength around 157 nm. Specifically, the polymers or high molecular weight compounds of the invention include recurring units of the following general formulae (1a) and (1b) or (1a), (1b) and (1c).

Herein, R¹, R², R to R⁷ and R¹⁰ to R¹² each are hydrogen, a fluorine atom or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R³ is a fluorine atom or a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms; R⁴ and R⁸ each are hydrogen or an acid labile group; R⁹ and R¹⁴ each are a fluorine atom or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R¹³ is —C(CF₃)₂—O—R¹⁵; R¹⁵ is hydrogen or an acid labile group; a, b and c are numbers in the range: 0<a<1, 0<b<1, 0≦c <1, and 0<a+b+c<1; d is an integer of 1 to 4; e and f each are an integer of 0 to 5, and 1e+f≦5.

Suitable straight, branched or cyclic alkyl groups are of 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms, especially 1 to 10 carbon atoms and include, but are not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, and n-octyl.

Suitable fluorinated alkyl groups correspond to the foregoing alkyl groups in which some or all of the hydrogen atoms are substituted with fluorine atoms, and include, for example, trifluoromethyl, 2,2,2-trifluoroethyl, 3,3,3-trifluoropropyl, 1,1,1,3,3,3-hexafluoroisopropyl, 1,1,2,2,3,3,3-heptafluoropropyl, and 2,2,3,3,4,4,5,5-octafluoropentyl. Groups of the following formulae are also useful.

Herein, R¹⁶ is hydrogen, a fluorine atom, a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, and g is an integer of 0 to 10.

The acid labile groups represented by R⁴, R⁸ and R¹⁵ are now described. It is noted that the invention requires that at least one of R⁴, R⁸ and R¹⁵ be an acid labile group. It is preferred that the polymer of the invention have at least one acid labile group. The acid labile groups are selected from a variety of such groups, preferably from among the groups of the following formulae (2) to (4).

In formula (2), R¹⁷ is a tertiary alkyl group of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, and h is an integer of 0 to 10. Illustrative, non-limiting, examples of the acid labile group of formula (2) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl, 1, 1-diethylpropyloxycarbonyl, 1,1-diethylpropyloxycarbonyl-methyl, 1-ethylcyclopentyloxycarbonyl, 1-ethylcyclopentyl-oxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl, 1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxy-carbonylmethyl, 2-tetrahydropyranyloxycarbonylmethyl, and 2-tetrahydrofuranyloxycarbonylmethyl groups.

In formula (3), R¹⁸ and R¹⁹ are hydrogen or straight, branched or cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylcyclohexyl and n-octyl. R²⁰ is a monovalent hydrocarbon group of 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, which may contain a hetero atom such as oxygen, for example, straight, branched or cyclic alkyl groups and substituted ones of these alkyl groups in which some hydrogen atoms are substituted with hydroxyl, alkoxy, oxo, amino or alkylamino groups. A pair of R¹⁸ and R¹⁹, a pair of R¹⁸ and R²⁰, or a pair of R¹⁹ and R²⁰, taken together, may form a ring. Each of R¹⁸, R¹⁹ and R²⁰ is a straight or branched alkylene group of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, which may contain a hetero atom such as oxygen, when they form a ring.

Of the acid labile groups of formula (3), cyclic ones are exemplified by tetrahydrofuran-2-yl, 2-methyltetrahydro-furan-2-yl, tetrahydropyran-2-yl, and 2-methyltetrahydro-pyran-2-yl. Of the acid labile groups of formula (3), straight or branched ones are exemplified below. Of these, ethoxyethyl, butoxyethyl and ethoxypropyl groups are preferred.

In formula (4), R²¹ to R²³ each are a straight, branched or cyclic alkyl group of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, examples of which are as described for R¹⁸ and R¹⁹. A pair of R²¹ and R²², R²¹ and R²³, and R²² and R²⁴, taken together, may form a ring.

Examples of the tertiary alkyl group represented by formula (4) include tert-butyl, triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl, 1-ethylcyclopentyl, 2-(2-methyl)amantyl, 2-(2-ethyl)adamantyl, tert-amyl, 1,1,1,3,3,3-hexafluoro-2-methyl-isopropyl, and 1,1,1,3,3,3-hexafluoro-2-cyclohexyl-isopropyl. Other illustrative examples of the tertiary alkyl group are given below.

In the above formulae, R²⁴ is a straight, branched or cyclic alkyl group of 1 to 6 carbon atoms; R²⁵ is a straight, branched or cyclic alkyl group of 2 to 6 carbon atoms; R²⁶ and R²⁷ each are hydrogen, a monovalent hydrocarbon group of 1 to 6 carbon atoms which may contain a hetero atom, or a monovalent hydrocarbon group of 1 to 6 carbon atoms which may be separated by a hetero atom. The hetero atom is typically selected from oxygen, sulfur and nitrogen atoms. The hetero atom is contained or intervenes in the form of —OH, —OR²⁸, —O—, —S—, —S(═O)—, —NH₂, —NHR²⁸, —N(R²⁸)₂, —NH— or —NR²⁸— wherein R²⁸ is a straight, branched or cyclic alkyl group of 1 to 10 carbon atoms.

Illustrative examples of R²⁴ include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, cyclopropyl, cyclopropylmethyl, cyclobutyl, cyclopentyl, and cyclohexyl. Illustrative examples of R²⁵ include ethyl, propyl, isopropyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, cyclopropyl, cyclopropylmethyl, cyclobutyl, cyclopentyl and cyclohexyl. Illustratively, R²⁶ and R²⁷ are hydrogen, straight, branched or cyclic alkyl groups, hydroxyalkyl groups, alkoxy groups and alkoxyalkyl groups, examples of which include methyl, hydroxymethyl, ethyl, hydroxyethyl, n-propyl, isopropyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, methoxy, methoxymethoxy, ethoxy, and tert-butoxy.

Illustrative structures of formula (1b) are given below.

Herein, R⁸ is hydrogen or an acid labile group as defined above.

Illustrative structures of formula (1c) are given below.

Herein, R¹⁵ is hydrogen or an acid labile group as defined above.

The polymers comprising recurring units of formulae (1a), (1b) and (c) according to the invention are fully adherent to substrates. Any of the recurring units shown below may be copolymerized into the inventive polymers for further enhancing the adhesion.

Herein, R⁰ is a straight, branched or cyclic alkyl group of 1 to 10 carbon atoms.

In formulae (1a), (1b) and (1c), a, b and c are numbers in the range: 0<a<1, 0<b<1, 0≦c<1, and 0 <a+b+c<1. Desirably a to c further satisfy the range: 0.1≦a/(a+b+c)≦0.7, more desirably 0.2≦a/(a+b+c)≦0.6, 0.2≦b/(a+b+c)≦0.8, more desirably 0.3≦b/(a+b+c)≦0.7, and 0≦c/(a+b+c)≦0.5, more desirably 0≦c/(a+b+c)≦0.3. Where recurring units originating from the adhesion-improving monomer, represented by (Q)_(h), are included in addition to the units of formulae (1a), (1b) and (1 c), it is preferred that (a+b+c)/(a+b+c+h) be from 0.7 to 1, more preferably from 0.8 to 1.

The polymer of the invention is generally synthesized by dissolving monomers corresponding to the respective units of formulae (1a), (1b) and (1 c) and optionally, an adhesion-improving monomer as mentioned above in a solvent, adding a catalyst thereto, and effecting polymerization reaction while heating or cooling the system if necessary. The polymerization reaction depends on the type of initiator or catalyst, trigger means (including light, heat, radiation and plasma), and polymerization conditions (including temperature, pressure, concentration, solvent, and additives). Commonly used for preparation of the polymer of the invention are radical polymerization of triggering polymerization with radicals of α,α′-azobisisobutyronitrile (AIBN) or the like, and ion (anion) polymerization using catalysts such as alkyl lithium. These polymerization steps may be carried out in their conventional manner.

The radical polymerization initiator used herein is not critical. Exemplary initiators include azo compounds such as 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobisiso-butyronitrile, and 2,2′-azobis(2,4,4-trimethylpentane); and peroxide compounds such as tert-butyl peroxypivalate, lauroyl peroxide, benzoyl peroxide and tert-butyl peroxy-laurate. Water-soluble initiators include persulfate salts such as potassium persulfate, and redox combinations of potassium persulfate or peroxides such as hydrogen peroxide with reducing agents such as sodium sulfite. The amount of the polymerization initiator used is determined as appropriate in accordance with such factors as the identity of initiator and polymerization conditions, although the amount is often in the range of about 0.001 to 5% by weight, especially about 0.01 to 2% by weight based on the total weight of monomers to be polymerized.

For the polymerization reaction, a solvent may be used. The polymerization solvent used herein is preferably one which does not interfere with the polymerization reaction. Typical solvents include ester solvents such as ethyl acetate and n-butyl acetate, ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone, aliphatic or aromatic hydrocarbon solvents such as toluene, xylene and cyclohexane, alcohol solvents such as isopropyl alcohol and ethylene glycol monomethyl ether, and ether solvents such as diethyl ether, dioxane, and tetrahydrofuran. These solvents may be used alone or in admixture of two or more. Further, any of well-known molecular weight modifiers such as dodecylmercaptan may be used in the polymerization system.

The temperature of polymerization reaction varies in accordance with the identity of polymerization initiator and the boiling point of the solvent although it is often preferably in the range of about 20 to 200° C., and especially about 50 to 140° C. Any desired reactor or vessel may be used for the polymerization reaction.

From the solution or dispersion of the polymer thus obtained, the organic solvent or water serving as the reaction medium is removed by any of well-known techniques. Suitable techniques include, for example, re-precipitation followed by filtration, and heat distillation under vacuum.

Desirably the polymer has a weight average molecular weight of about 1,000 to about 1,000,000, and especially about 2,000 to about 100,000.

The polymer of the invention can be used as a base resin in resist compositions, specifically chemical amplification type resist compositions, and especially chemical amplification type positive working resist compositions. It is understood that the polymer of the invention may be admixed with another polymer for the purpose of altering the dynamic properties, thermal properties, alkali solubility and other physical properties of polymer film. The type of the other polymer which can be admixed is not critical. Any of polymers known to be useful in resist use may be admixed in any desired proportion.

Resist Composition

As long as the polymer of the invention is used as a base resin, the resist composition of the invention may be prepared using well-known components. In a preferred embodiment, the chemically amplified positive resist composition is defined as comprising (A) the above-defined polymer as a base resin, (B) an organic solvent, and (C) a photoacid generator. In the resist composition, there may be further formulated (D) a basic compound and/or (E) a dissolution inhibitor.

Component (B)

The organic solvent used as component (B) in the invention may be any organic solvent in which the base resin (inventive polymer), photoacid generator, and other components are soluble. Illustrative, non-limiting, examples of the organic solvent include ketones such as cyclohexanone and methyl-2-n-amylketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; and esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate.

Also useful are fluorinated organic solvents. Examples include 2-fluoroanisole, 3-fluoroanisole, 4-fluoroanisole, 2,3-difluoroanisole, 2,4-difluoroanisole, 2,5-difluoroanisole, 5,8-difluoro-1,4-benzodioxane, 2,3-difluorobenzyl alcohol, 1,3-difluoro-2-propanol, 2′,4′-difluoropropiophenone, 2,4-difluorotoluene, trifluoroacetaldehyde ethyl hemiacetal, trifluoroacetamide, trifluoroethanol, 2,2,2-trifluoroethyl butyrate, ethyl heptafluorobutyrate, ethyl heptafluorobutylacetate, ethyl hexafluoroglutarylmethyl, ethyl 3-hydroxy-4,4,4-trifluoro-butyrate, ethyl 2-methyl-4,4,4-trifluoroacetoacetate, ethyl pentafluorobenzoate, ethyl pentafluoropropionate, ethyl pentafluoropropynylacetate, ethyl perfluorooctanoate, ethyl 4,4,4-trifluoroacetoacetate, ethyl 4,4,4-trifluorobutyrate, ethyl 4,4,4-trifluorocrotonate, ethyl trifluorosulfonate, ethyl 3-(trifluoromethyl)butyrate, ethyl trifluoropyruvate, sec-ethyl trifluoroacetate, fluorocyclohexane, 2,2,3,3,4,4,4-heptafluoro-1-butanol, 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione, 1,1,1,3,5,5,5-heptafluoropentane-2,4-dione, 3,3,4,4,5,5,5-heptafluoro-2-pentanol, 3,3,4,4,5,5,5-heptafluoro-2-pentanone, isopropyl 4,4,4-trifluoroacetoacetate, methyl perfluorodecanoate, methyl perfluoro(2-methyl-3-oxahexanoate), methyl perfluorononanoate, methyl perfluorooctanoate, methyl 2,3,3,3-tetrafluoropropionate, methyl trifluoroacetoacetate, 1,1,1,2,2,6,6,6-octafluoro-2,4-hexanedione, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, 1H,1H,2H,2H-perfluoro-1-decanol, perfluoro-2,5-dimethyl-3,6-dioxane anionic acid methyl ester, 2H-perfluoro-5-methyl-3,6-dioxanonane, 1H,1H,2H,3H,3H-perfluorononane-1,2-diol, 1H,1H,9H-perfluoro-1-nonanol, 1H,1H-perfluorooctanol, -1H,1H,2H,2H-perfluorooctanol, 2H-perfluoro-5,8,11,14-tetramethyl-3,6,9,12,15-pentaoxaoctadecane, perfluorotributylamine, perfluorotrihexylamine, methyl perfluoro-2,5,8-trimethyl-3,6,9-trioxadodecanoate, perfluorotripentylamine, perfluorotripropylamine, 1H,1H,2H,3H,3H-perfluoroundecane-1,2-diol, trifluorobutanol-1,1,1-trifluoro-5-methyl-2,4-hexanedione, 1,1,1-trifluoro-2-propanol, 3,3,3-trifluoro-1-propanol, 1,1,1-trifluoro-2-propyl acetate, perfluorobutyltetrahydrofuran, perfluorodecalin, perfluoro(1,2-dimethylcyclohexane), -perfluoro(1,3-dimethylcyclohexane), propylene glycol trifluoromethyl ether acetate, propylene glycol methyl ether trifluoromethyl acetate, butyl trifluoromethylacetate, methyl 3-trifluoromethoxypropionate, perfluorocyclohexanone, propylene glycol trifluoromethyl ether, butyl trifluoroacetate, and 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione.

These solvents may be used alone or in combinations of two or more thereof. Of the above organic solvents, preferred are diethylene glycol dimethyl ether and 1-ethoxy-2-propanol, in which the photoacid generator is most soluble, and propylene glycol monomethyl ether acetate which is safe, and mixtures thereof.

The solvent is preferably used in an amount of about 300 to 10,000 parts by weight, more preferably about 500 to 5,000 parts by weight per 100 parts by weight of the base resin.

Component (C)

Suitable examples of the photoacid generator (C) include onium salts of general formula (5) below, diazomethane derivatives of formula (6), glyoxime derivatives of formula (7), β-ketosulfone derivatives, disulfone derivatives, nitrobenzylsulfonate derivatives, sulfonic acid ester derivatives, and imidoyl sulfonate derivatives.

The onium salts used as the photoacid generator are of the general formula (5). (R²⁹)_(j)M⁺K⁻  (5)

In the formula, R²⁹ is a straight, branched or cyclic alkyl of 1 to 12 carbon atoms, an aryl of 6 to 20 carbon atoms, or an aralkyl of 7 to 12 carbon atoms; M⁺ is iodonium or sulfonium; K⁻ is a non-nucleophilic counter-ion; and the letter j is 2 or 3.

Illustrative examples of alkyl groups represented by R²⁹ include methyl, ethyl, propyl, butyl, pentyl, 2-oxocyclopentyl, norbornyl, and adamantyl. Exemplary aryl groups include phenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl. Exemplary aralkyl groups include benzyl and phenethyl. Examples of the non-nucleophilic counter-ion represented by K⁻ include halide ions such as chloride and bromide; fluoroalkylsulfonate ions such as triflate, 1,1, 1-trifluoroethanesulfonate, and nonafluorobutane-sulfonate; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; and alkylsulfonate ions such as mesylate and butanesulfonate.

Illustrative examples of the onium salts include diphenyliodonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)phenyliodonium trifluoromethanesulfonate, diphenyliodonium p-toluenesulfonate, (p-tert-butoxyphenyl)-phenyliodonium p-toluenesulfonate, triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenyl-sulfonium trifluoromethanesulfonate, bis(p-tert-butoxy-phenyl)phenylsulfonium trifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxy-phenyl)diphenylsulfonium p-toluenesulfonate, bis(p-tert-butoxyphenyl)phenylsulfonium p-toluenesulfonate, tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate, triphenylsulfonium nonafluorobutanesulfonate, triphenyl-sulfonium butanesulfonate, trimethylsulfonium trifluoro-methanesulfonate, trimethylsulfonium p-toluenesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethane-sulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium p-toluenesulfonate, dimethylphenylsulfonium trifluoro-methanesulfonate, dimethylphenylsulfonium p-toluenesulfonate, dicyclohexylphenylsulfonium trifluoromethanesulfonate, dicyclohexylphenylsulfonium p-toluenesulfonate, trinaphthyl-sulfonium trifluoromethanesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, (2-norbornyl)methyl(2-oxocyclohexyl)sulfonium trifluoro-methanesulfonate, ethylenebis[methyl(2-oxocyclopentyl)-sulfonium trifluoromethanesulfonate], and 1,21-naphthyl-carbonylmethyltetrahydrothiophenium triflate.

The diazomethane derivatives used as the photoacid generator are of the general formula (6).

In the formula, R³⁰ and R³¹ are straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 12 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms.

Illustrative examples of alkyl groups represented by R³⁰ and R³¹ include methyl, ethyl, propyl, butyl, amyl, cyclopentyl, cyclohexyl, norbornyl, and adamantyl. Exemplary halogenated alkyl groups include trifluoromethyl, 2,2,2-trifluoroethyl, 2,2,2-trichloroethyl, and nonafluoro-butyl. Exemplary aryl groups include phenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxy-phenyl, ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl. Exemplary halogenated aryl groups include fluorophenyl, chlorophenyl, and 1,2,3,4,5-pentafluorophenyl. Exemplary aralkyl groups include benzyl and phenethyl. -Examples of the diazomethane derivatives include bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)-diazomethane, bis(xylenesulfonyl)diazomethane, bis(cyclo-hexylsulfonyl)diazomethane, bis(cyclopentylsulfonyl)diazo-methane, bis(n-butylsulfonyl)diazomethane, bis(isobutyl-sulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)-diazomethane, bis(tert-butylsulfonyl)diazomethane, bis(n-amylsulfonyl)diazomethane, bis(isoamylsulfonyl)diazo-methane, bis(sec-amylsulfonyl)diazomethane, bis(tert-amylsulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-butylsulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-amylsulfonyl)diazomethane, and 1-tert-amylsulfonyl-1-(tert-butylsulfonyl)diazomethane.

The glyoxime derivatives used as the photoacid generator are of the general formula (7).

In the formula, R³² to R³⁴ are straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 12 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms. R³³ and R³⁴ may together form a cyclic structure with the proviso that if they form a cyclic structure, each is a straight or branched alkylene group of 1 to 6 carbon atoms.

The alkyl, halogenated alkyl, aryl, halogenated aryl, and aralkyl groups represented by R³² to R³⁴ are exemplified by the same groups as mentioned above for R³⁰ and R³¹. Examples of alkylene groups represented by R³³ and R³⁴ include methylene, ethylene, propylene, butylene, and hexylene.

Examples of the glyoxime derivatives include

-   bis-O-(p-toluenesulfonyl)-α-dimethylglyoxime, -   bis-O-(p-toluenesulfonyl)-α-diphenylglyoxime, -   bis-O-(p-toluenesulfonyl)-α-dicyclohexylglyoxime, -   bis-O-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime, -   bis-O-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, -   bis-O-(n-butanesulfonyl)-α-dimethylglyoxime, -   bis-O-(n-butanesulfonyl)-α-diphenylglyoxime, -   bis-O-(n-butanesulfonyl)-α-dicyclohexylglyoxime, -   bis-0-(n-butanesulfonyl)-2,3-pentanedioneglyoxime, -   bis-O-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, -   bis-O-(methanesulfonyl)-α-dimethyleglyoxime, -   bis-O-(trifluoromethanesulfonyl)-α-dimethylglyoxime, -   bis-O-(1,1,1-trifluoroethanesulfonyl)-α-dimethylglyoxime, -   bis-O-(tert-butanesulfonyl)-α-dimethylglyoxime, -   bis-O-(perfluorooctanesulfonyl)-α-dimethylglyoxime, -   bis-O-(cyclohexanesulfonyl)-α-dimethylglyoxime, -   bis-O-(benzenesulfonyl)-α-dimethylglyoxime, -   bis-O-(p-fluorobenzenesulfonyl)-α-dimethylglyoxime, -   bis-O-(p-tert-butylbenzenesulfonyl)-α-dimethylglyoxime, -   bis-O-(xylenesulfonyl)-α-dimethylglyoxime, and -   bis-O-(camphorsulfonyl)-α-dimethylglyoxime.

Other useful photoacid generators include β-ketosulfone derivatives such as 2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane and 2-isopropylcarbonyl-2-(p-toluenesulfonyl)propane; disulfone derivatives such as diphenyl disulfone and dicyclohexyl disulfone; nitrobenzyl sulfonate derivatives such as 2,6-dinitrobenzyl p-toluene-sulfonate and 2,4-dinitrobenzyl p-toluenesulfonate; sulfonic acid ester derivatives such as 1,2,3-tris(methanesulfonyl-oxy)benzene, 1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and 1,2,3-tris(p-toluenesulfonyloxy)benzene; and imidoyl sulfonate derivatives such as phthalimidoyl triflate, phthalimidoyl tosylate, 5-norbornene-2,3-dicarboxyimidoyl triflate, 5-norbornene-2,3-dicarboxyimidoyl tosylate, and 5-norbornene-2,3-dicarboxyimidoyl n-butylsulfonate.

Preferred among these photoacid generators are onium salts such as triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethane-sulfonate, tris(p-tert-butoxyphenyl)sulfonium trifluoro-methanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate, cyclohexyl-methyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, (2-norbornyl)methyl(2-oxocylohexyl)sulfonium trifluoro-methanesulfonate, and 1,21-naphthylcarbonylmethyltetrahydro-thiophenium triflate; diazomethane derivatives such as bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)-diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)-diazomethane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)-diazomethane, and bis(tert-butylsulfonyl)diazomethane; and glyoxime derivatives such as bis-O-(p-toluenesulfonyl)-α-dimethylglyoxime and bis-O-(n-butanesulfonyl)-α-dimethyl-glyoxime. These photoacid generators may be used singly or in combinations of two or more thereof. Onium salts are effective for improving rectangularity, while diazomethane derivatives and glyoxime derivatives are effective for reducing standing waves. The combination of an onium salt with a diazomethane or a glyoxime derivative allows for fine adjustment of the profile.

The photoacid generator is preferably added in an amount of about 0.2 to 15 parts by weight per 100 parts by weight of the base resin. At less than 0.2 part, the amount of acid generated during exposure would be too small and the sensitivity and resolution be poor, whereas the addition of more than 15 parts would lower the transmittance of the resist and result in a poor resolution.

Component (D)

The basic compound used as component (D) is preferably a compound capable of suppressing the rate of diffusion when the acid generated by the photoacid generator diffuses within the resist film. The inclusion of this type of basic compound holds down the rate of acid diffusion within the resist film, resulting in better resolution. In addition, it suppresses changes in sensitivity following exposure, thus reducing substrate and environment dependence, as well as improving the exposure latitude and the pattern profile. See JP-A 5-232706, 5-249683, 5-158239, 5-249662, 5-257282, 5-289322, and 5-289340.

Examples of suitable basic compounds include ammonia, primary, secondary, and tertiary aliphatic amines, mixed amines, aromatic amines, heterocyclic amines, carboxyl group-bearing nitrogenous compounds, sulfonyl group-bearing nitrogenous compounds, hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, alcoholic nitrogenous compounds, amide derivatives, and imide derivatives.

Examples of suitable primary aliphatic amines include methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, iso-butylamine, sec-butylamine, tert-butylamine, pentylamine, tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine, heptylamine, octylamine, nonylamine, decylamine, dodecylamine, cetylamine, methylenediamine, ethylenediamine, and tetraethylene-pentamine. Examples of suitable secondary aliphatic amines include dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, di-n-butylamine, di-iso-butylamine, di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine, dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, didodecylamine, dicetylamine, N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, and N,N-dimethyltetraethylenepentamine. Examples of suitable tertiary aliphatic amines include trimethylamine, triethylamine, tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine, tri-iso-butylamine, tri-sec-butylamine, tripentylamine, tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, tridodecylamine, tricetylamine, N,N,N′,N′-tetramethylmethylenediamine, N,N,N′,N′-tetra-methylethylenediamine, and N,N,N′,N′-tetramethyltetra-ethylenepentamine.

Examples of suitable mixed amines include dimethyl-ethylamine, methylethylpropylamine, benzylamine, phenethyl-amine, and benzyldimethylamine. Examples of suitable aromatic amines include aniline derivatives (e.g., aniline, N-methylaniline, N-ethylaniline, N-propylaniline, N,N-dimethylaniline, 2-methylaniline, 3-methylaniline, 4-methylaniline, ethylaniline, propylaniline, trimethyl-aniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline, 2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, and N,N-dimethyltoluidine), diphenyl(p-tolyl)amine, methyldiphenylamine, triphenylamine, phenylenediamine, naphthylamine, and diaminonaphthalene. Examples of suitable heterocyclic amines include pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole, 2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazole derivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g., thiazole and isothiazole), imidazole derivatives (e.g., imidazole, 4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazole derivatives, furazan derivatives, pyrroline derivatives (e.g., pyrroline and 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine, N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone), imidazoline derivatives, imidazolidine derivatives, pyridine derivatives (e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine, butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine, trimethyl-pyridine, triethylpyridine, phenylpyridine, 3-methyl-2-phenylpyridine, 4-tert-butylpyridine, diphenylpyridine, benzylpyridine, methoxypyridine, butoxypyridine, dimethoxy-pyridine, 1-methyl-2-pyridine, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine, 2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine), pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives, pyrazoline derivatives, pyrazolidine derivatives, piperidine derivatives, piperazine derivatives, morpholine derivatives, indole derivatives, isoindole derivatives, 1H-indazole derivatives, indoline derivatives, quinoline derivatives (e.g., quinoline and 3-quinolinecarbonitrile), isoquinoline derivatives, cinnoline derivatives, quinazoline derivatives, quinoxaline derivatives, phthalazine derivatives, purine derivatives, pteridine derivatives, carbazole derivatives, phenanthridine derivatives, acridine derivatives, phenazine derivatives, 1,10-phenanthroline derivatives, adenine derivatives, adenosine derivatives, guanine derivatives, guanosine derivatives, uracil derivatives, and uridine derivatives.

Examples of suitable carboxyl group-bearing nitrogenous compounds include aminobenzoic acid, indolecarboxylic acid, nicotinic acid, and amino acid derivatives (e.g. alanine, alginine, aspartic acid, glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine, methionine, phenylalanine, threonine, lysine, 3-aminopyrazine-2-carboxylic acid, and methoxyalanine).

Examples of suitable sulfonyl group-bearing nitrogenous compounds include 3-pyridinesulfonic acid and pyridinium p-toluenesulfonate.

Examples of suitable hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, and alcoholic nitrogenous compounds include 2-hydroxypyridine, aminocresol, 2,4-quinolinediol, 3-indolemethanol hydrate, monoethanolamine, diethanolamine, triethanolamine, N-ethyldiethanolamine, N,N-diethylethanol-amine, triisopropanolamine, 2,2′-iminodiethanol, 2-aminoethanol, 3-amino-1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine, 2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine, 1-[2-(2-hydroxyethoxy)ethyl]-piperazine, piperidine ethanol, 1-(2-hydroxyethyl)-pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone, 3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol, 8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidine ethanol, 1-aziridine ethanol, N-(2-hydroxy-ethyl)phthalimide, and N-(2-hydroxyethyl)isonicotinamide.

Examples of suitable amide derivatives include formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, and benzamide. Suitable imide derivatives include phthalimide, succinimide, and maleimide.

In addition, basic compounds of the following general formula (8) may also be included alone or in admixture.

In the formula, k is equal to 1, 2 or 3. The side chains R³⁵ may be the same or different, may bond together to form a ring and are represented by the formula (8a), (8b) or (8c). The side chains R³⁶ may be the same or different, and are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms which may contain a hydroxyl group or ether. R³⁷, R³⁹ and R⁴² each are a straight or branched alkylene group of 1 to 4 carbon atoms. R³⁸ and R⁴¹ each are hydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain at least one hydroxyl, ether or ester group or lactone ring. R⁴⁰ is a single bond or a straight or branched alkylene group of 1 to 4 carbon atoms; and R⁴³ is a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain at least one hydroxyl, ether or ester group or lactone ring.

Illustrative examples of the compounds of formula (8) include tris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxy-ethoxy)ethyl}amine, tris{2-(2-methoxyethoxymethoxy)ethyl}-amine, tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}-amine, tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine, 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, 4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane, 1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane, 1-aza-12-crown-4, 1-aza-15-crown-5, 1-aza-18-crown-6, tris(2-formyloxyethyl)amine, tris(2-acetoxyethyl)amine, tris(2-propionyloxyethyl)amine, tris(2-butyryloxyethyl)amine, tris(2-isobutyryloxyethyl)amine, tris(2-valeryloxyethyl)-amine, tris(2-pivaloyloxyethyl)amine, N,N-bis(2-acetoxy-ethyl)-2-(acetoxyacetoxy)ethylamine, tris(2-methoxycarbonyl-oxyethyl)amine, tris(2-tert-butoxycarbonyloxyethyl)amine, tris[2-(2-oxopropoxy)ethyl]amine, tris[2-(methoxycarbonyl-methyl)oxyethyl]amine, tris[2-(tert-butoxycarbonylmethyl-oxy)ethyl]amine, tris[2-(cyclohexyloxycarbonylmethyloxy)-ethyl]amine, tris(2-methoxycarbonylethyl)amine, tris(2-ethoxycarbonylethyl)amine, N,N-bis(2-hydroxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(ethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(ethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-methoxyethoxyca N,N-bis(2-hydroxy-ethyl)-2-(2-hydroxyethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-acetoxyethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-[(methoxycarbonyl)methoxy-carbonyl]ethylamine, N,N-bis(2-acetoxyethyl)-2-[(methoxy-carbonyl)methoxycarbonyl]ethylamine, N,N-bis(2-hydroxy-ethyl)-2-(2-oxopropoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)-ethylamine, N,N-bis(2-hydroxyethyl)-2-[(2-oxotetrahydro-furan-3-yl)oxycarbonyl]ethylamine, N,N-bis(2-acetoxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]ethylamine, N,N-bis(2-hydroxyethyl)-2-(4-hydroxybutoxycarbonyl)ethyl-amine, N,N-bis(2-formyloxyethyl)-2-(4-formyloxybutoxy-carbonyl)ethylamine, N,N-bis(2-formyloxyethyl)-2-(2-formyloxyethoxycarbonyl)ethylamine, N,N-bis(2-methoxyethyl)-2-(methoxycarbonyl)eth N-(2-hydroxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(2-acetoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(2-hydroxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine, N-(2-acetoxyethyl)-bis[2-(ethoxycarbonyl)ethyl]ami N-(3-hydroxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(3-acetoxy-1-propyl)-bis[2-(methoxycarbo amine, N-(2-methoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-butyl-bis[2-(methoxy-carbonyl)ethyl]amine, N-butyl-bis[2-(2-methoxyethoxy-carbonyl)ethyl]amine, N-methyl-bis(2-acetoxyethyl)amine, N-ethyl-bis(2-acetoxyethyl)amine, N-methyl-bis(2-pivaloyl-oxyethyl)amine, N-ethyl-bis[2-(methoxycarbonyloxy)ethyl]-amine, N-ethyl-bis[2-(tert-butoxycarbonyloxy)ethyl]amine, tris(methoxycarbonylmethyl)amine, tris(ethoxycarbonyl-methyl)amine, N-butyl-bis(methoxycarbonylmethyl)amine, N-hexyl-bis(methoxycarbonylmethyl)amine, and β-(diethylamino)-δ-valerolactone.

Also useful are one or more of cyclic structure-bearing basic compounds having the following general formula (9).

Herein R³⁵ is as defined above, and R⁴⁴ is a straight or branched alkylene group of 2 to 20 carbon atoms which may contain one or more carbonyl, ether, ester or sulfide groups.

Illustrative examples of the cyclic structure-bearing basic compounds having formula (9) include 1-[2-(methoxy-methoxy)ethyl]pyrrolidine, 1-[2-(methoxymethoxy)ethyl]-piperidine, 4-[2-(methoxymethoxy)ethyl]morpholine, 1-[2-[(2-methoxyethoxy)methoxy]ethyl]pyrrolidine, 1-[2-[(2-methoxyethoxy)methoxy]ethyl]piperidine, 4-[2-[(2-methoxyethoxy)methoxy]ethyl]morpholine, 2-(1-pyrrolidinyl)ethyl acetate, 2-piperidinoethyl acetate, 2-morpholinoethyl acetate, 2-(1-pyrrolidinyl)ethyl formate, 2-piperidinoethyl propionate, 2-morpholinoethyl acetoxyacetate, 2-(1-pyrrolidinyl)ethyl methoxyacetate, 4-[2-(methoxycarbonyloxy)ethyl]morpholine, 1-[2-(t-butoxycarbonyloxy)ethyl]piperidine, 4-[2-(2-methoxyethoxycarbonyloxy)ethyl]morpholine, methyl 3-(1-pyrrolidinyl)propionate, methyl 3-piperidinopropionate, methyl 3-morpholinopropionate, methyl 3-(thiomorpholino)-propionate, methyl 2-methyl-3-(1-pyrrolidinyl)propionate, ethyl 3-morpholinopropionate, methoxycarbonylmethyl 3-piperidinopropionate, 2-hydroxyethyl 3-(1-pyrrolidinyl)-propionate, 2-acetoxyethyl 3-morpholinopropionate, 2-oxotetrahydrofuran-3-yl 3-(l-pyrrolidinyl)propionate, tetrahydrofurfuryl 3-morpholinopropionate, glycidyl 3-piperidinopropionate, 2-methoxyethyl 3-morpholino-propionate, 2-(2-methoxyethoxy)ethyl 3-(1-pyrrolidinyl)-propionate, butyl 3-morpholinopropionate, cyclohexyl 3-piperidinopropionate, α-(1-pyrrolidinyl)methyl-γ-butyrolactone, β-piperidino-γ-butyrolactone, β-morpholino-δ-valerolactone, methyl 1-pyrrolidinylacetate, methyl piperidinoacetate, methyl morpholinoacetate, methyl thiomorpholinoacetate, ethyl 1-pyrrolidinylacetate, and 2-methoxyethyl morpholinoacetate.

Also, one or more of cyano-bearing basic compounds having the following general formulae (10) to (13) may be blended.

Herein, R³⁵, R⁴⁴ and k are as defined above, and R⁴⁵ and R⁴⁶ each are independently a straight or branched alkylene group of 1 to 4 carbon atoms.

Illustrative examples of the cyano-bearing basic compounds include 3-(diethylamino)propiononitrile, N,N-bis(2-hydroxyethyl)-3-aminopropiononitrile, N,N-bis(2-acetoxyethyl)-3-aminopropiononitrile, N,N-bis(2-formyloxyethyl)-3-aminopropiononitrile, N,N-bis(2-methoxyethyl)-3-aminopropiononitrile, N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropiononitrile, methyl N-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropionate, methyl N-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropionate, methyl N-(2-acetoxyethyl)-N-(2-cyanoethyl)-3-aminopropionate, N-(2-cyanoethyl)-N-ethyl-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropiononitrile, N-(2-acetoxyethyl)-N-(2-cyanoethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(2-formyloxyethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-[2-(methoxymethoxy)ethyl]-3-amino-propiononitrile, N-(2-cyanoethyl)-N-(3-hydroxy-1-propyl)-3-aminopropiononitrile, N-(3-acetoxy-1-propyl)-N-(2-cyanoethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(3-formyloxy-1-propyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-tetrahydrofurfuryl-3-aminopropiononitrile, N,N-bis(2-cyanoethyl)-3-aminopropiononitrile, diethylaminoacetonitrile, N,N-bis(2-hydroxyethyl)aminoaceto-nitrile, N,N-bis(2-acetoxyethyl)aminoacetonitrile, N,N-bis(2-formyloxyethyl)aminoacetonitrile, N,N-bis(2-methoxyethyl)aminoacetonitrile, N,N-bis[2-(methoxymethoxy)ethyl]aminoacetonitrile, methyl N-cyanomethyl-N-(2-methoxyethyl)-3-aminopropionate, methyl N-cyanomethyl-N-(2-hydroxyethyl)-3-aminopropionate, methyl N-(2-acetoxyethyl)-N-cyanomethyl-3-aminopropionate, N-cyanomethyl-N-(2-hydroxyethyl)aminoacetonitrile, N-(2-acetoxyethyl)-N-(cyanomethyl)aminoacetonitrile, N-cyanomethyl-N-(2-formyloxyethyl)aminoacetonitrile, N-cyanomethyl-N-(2-methoxyethyl)aminoacetonitrile, N-cyanomethyl-N-[2-(methoxymethoxy)ethyl)aminoacetonitrile, N-cyanomethyl-N-(3-hydroxy-1-propyl)aminoacetonitrile, N-(3-acetoxy-1-propyl)-N-(cyanomethyl)aminoacetonitrile, N-cyanomethyl-N-(3-formyloxy-1-propyl)aminoacetonitrile, N,N-bis(cyanomethyl)aminoacetonitrile, 1-pyrrolidine-propiononitrile, 1-piperidinepropiononitrile, 4-morpholinepropiononitrile, 1-pyrrolidineacetonitrile, 1-piperidineacetonitrile, 4-morpholineacetonitrile, cyanomethyl 3-diethylaminopropionate, cyanomethyl N,N-bis(2-hydroxyethyl)-3-aminopropionate, cyanomethyl N,N-bis(2-acetoxyethyl)-3-aminopropionate, cyanomethyl N,N-bis(2-formyloxyethyl)-3-aminopropionate, cyanomethyl N,N-bis(2-methoxyethyl)-3-aminopropionate, cyanomethyl N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropionate, 2-cyanoethyl 3-diethylaminopropionate, 2-cyanoethyl N,N-bis(2-hydroxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis(2-acetoxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis(2-formyloxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis(2-methoxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropionate, cyanomethyl 1-pyrrolidinepropionate, cyanomethyl 1-piperidinepropionate, cyanomethyl 4-morpholinepropionate, 2-cyanoethyl 1-pyrrolidinepropionate, 2-cyanoethyl 1-piperidinepropionate, and 2-cyanoethyl 4-morpholine-propionate.

The basic compound is preferably formulated in an amount of 0.001 to 2 parts, and especially 0.01 to 1 part by weight, per 100 parts by weight of the entire base resin. Less than 0.001 part of the basic compound may fail to achieve the desired effects thereof, while the use of more than 2 parts would result in too low a sensitivity.

Component (E)

The dissolution inhibitor (E) is a compound with a molecular weight of up to 3,000 which changes its solubility in an alkaline developer under the action of an acid. Typically, a compound obtained by partially or entirely substituting acid labile substituents on a phenol or carboxylic acid derivative having a molecular weight of up to 2,500 is added as the dissolution inhibitor. The acid labile groups may be either fluorinated ones contemplated herein or conventional fluorine-free ones.

Examples of the phenol or carboxylic acid derivative having a molecular weight of up to 2,500 include 4,4′-(1-methylethylidene)bisphenol, (1,11-biphenyl-4,4′-diol)-2,2′-methylenebis(4-methylphenol), 4,4-bis(4′-hydroxy-phenyl)valeric acid, tris(4-hydroxyphenyl)methane, 1,1,1-tris(4′-hydroxyphenyl)ethane, 1,1,2-tris(4′-hydroxy-phenyl)ethane, phenolphthalein, thimolphthalein, 3,3′-difluoro[(1,1′-biphenyl)-4,4′-diol], 3,3′,5,5¹-tetrafluoro[(1,1′-biphenyl)-4,4′-diol], 4,4′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]-bisphenol, 4,4′-methylenebis(2-fluorophenol), 2,2′-methylenebis(4-fluorophenol), 4,4′-isopropylidenebis(2-fluorophenol), cyclohexylidenebis(2-fluorophenol), 4,4′-[(4-fluorophenyl)methylene]bis(2-fluorophenol), 4,4′-methylene-bis(2,6-difluorophenol), 4,4′-(4-fluorophenyl)methylene-bis(2,6-difluorophenol), 2,6-bis[(2-hydroxy-5-fluorophenyl)-methyl]-4-fluorophenol, 2,6-bis[(4-hydroxy-3-fluorophenyl)-methyl]-4-fluorophenol, and 2,4-bis[(3-hydroxy-4-hydroxy-phenyl)methyl]-6-methylphenol. The acid labile substituents are the same as described above for formulae (2) to (4).

Illustrative, non-limiting, examples of the dissolution inhibitors which are useful herein include 3,3′, 5,5′-tetrafluoro[(1,1′-biphenyl)-4,4′-di-t-butoxy-carbonyl]4,4′-[2,2,2-trifluoro-1-(trifluoromethyl)-ethylidene]bisphenol-4,4′-di-t-butoxycarbonyl, bis(4-(2′-tetrahydropyranyloxy)phenyl)methane, bis(4-(2′-tetrahydro-furanyloxy)phenyl)methane, bis(4-tert-butoxyphenyl)methane, bis(4-tert-butoxycarbonyloxyphenyl)methane, bis(4-tert-butoxycarbonylmethyloxyphenyl)methane, bis(4-(1′-ethoxy-ethoxy)phenyl)methane, bis(4-(1′-ethoxypropyloxy)phenyl)-methane, 2,2-bis(4′-(2″-tetrahydropyranyloxy))propane, 2,2-bis(4′-(2″-tetrahydrofuranyloxy)phenyl)propane, 2,2-bis(4′-tert-butoxyphenyl)propane, 2,2-bis(4′-tert-butoxycarbonyloxyphenyl)propane, 2,2-bis(4-tert-butoxy-carbonylmethyloxyphenyl)propane, 2,2-bis(4′-(1″-ethoxy-ethoxy)phenyl)propane, 2,2-bis(4′-(1″-ethoxypropyloxy)-phenyl)propane, tert-butyl 4,4-bis(4′-(2″-tetrahydropyranyl-oxy tert-butyl 4,4-bis(4′-(2″-tetrahydro-furanyloxy)phenyl)valerate, tert-butyl 4,4-bis(4′-tert-butoxyphenyl)valerate, tert-butyl 4,4-bis(4-tert-butoxy-carbonyloxyphenyl)valerate, tert-butyl 4,4-bis(4′-tert-butoxycarbonylmethyloxyphenyl)valerate, tert-butyl 4,4-bis(4′-(1″-ethoxyethoxy)phenyl)valerate, tert-butyl 4,4-bis(4′-(1″-ethoxypropyloxy)phenyl)valerate, tris(4-(2′-tetrahydropyranyloxy)phenyl)methane, tris(4-(2′-tetrahydro-furanyloxy)phenyl)methane, tris(4-tert-butoxyphenyl)methane, tris(4-tert-butoxycarbonyloxyphenyl)methane, tris(4-tert-butoxycarbonyloxymethylphenyl)methane, tris(4-(1′-ethoxy-ethoxy)phenyl)methane, tris(4-(1′-ethoxypropyloxy)phenyl)-methane, 1,1,2-tris(4′-(2″-tetrahydropyranyloxy)phenyl)-ethane, 1,1,2-tris(4′-(2″-tetrahydrofuranyloxy)phenyl)ethane, 1,1,2-tris(4′-tert-butoxyphenyl)ethane, 1,1,2-tris(4′-tert-butoxycarbonyloxyphenyl)ethane, 1,1,2-tris(4′-tert-butoxy-carbonylmethyloxyphenyl)ethane, 1,1,2-tris(4′-(1′-ethoxy-ethoxy)phenyl)ethane, 1,1,2-tris(4′-(1′-ethoxypropyloxy)-phenyl)ethane, t-butyl 2-trifluoromethylbenzenecarboxylate, t-butyl 2-trifluoromethylcyclohexanecarboxylate, t-butyl decahydronaphthalene-2,6-dicarboxylate, t-butyl cholate, t-butyl deoxycholate, t-butyl adamantanecarboxylate, t-butyl adamantaneacetate, and tetra-t-butyl 1,1′-bicyclohexyl-3,3′,4,4′-tetracarboxylate.

In the resist composition according to the invention, an appropriate amount of the dissolution inhibitor (E) is up to about 20 parts, and especially up to about 15 parts by weight per 100 parts by weight of the base resin in the composition. With more than 20 parts of the dissolution inhibitor, the resist composition becomes less heat resistant because of an increased content of monomer components.

The resist composition of the invention may include optional ingredients, typically a surfactant which is commonly used for improving the coating characteristics. Optional ingredients may be added in conventional amounts so long as this does not compromise the objects of the invention.

A nonionic surfactant is preferred, examples of which include perfluoroalkyl polyoxyethylene ethanols, fluorinated alkyl esters, perfluoroalkylamine oxides, perfluoroalkyl EO-addition products, and fluorinated organosiloxane compounds. Illustrative examples include Florade FC-430 and FC-431 from Sumitomo 3M Ltd., Surflon S-141 and S-145 from Asahi Glass Co., Ltd., Unidyne DS-401, DS-403, and DS-451 from Daikin Industries Ltd., Megaface F-8151 from Dainippon Ink & Chemicals, Inc., and X-70-092 and X-70-093 from Shin-Etsu Chemical Co., Ltd. Preferred surfactants include Florade FC-430 from Sumitomo 3M Ltd. and X-70-093 from Shin-Etsu Chemical Co., Ltd.

Pattern formation using the resist composition of the invention may be carried out by a known lithographic technique. For example, the resist composition may be applied onto a substrate such as a silicon wafer by spin coating or the like to form a resist film having a thickness of 0.1 to 1.0 μm, which is then pre-baked on a hot plate at 60 to 200° C. for 10 seconds to 10 minutes, and preferably at 80 to 150° C. for ½ to 5 minutes. A patterning mask having the desired pattern may then be placed over the resist film, and the film exposed through the mask to an electron beam or to high-energy radiation such as deep-UV rays, excimer laser beams, or x-rays in a dose of about I to 200 mJ/cm², and preferably about 10 to 100 mJ/cm², then post-exposure baked (PEB) on a hot plate at 60 to 150° C. for 10 seconds to 5 minutes, and preferably at 80 to 130° C. for ½ to 3 minutes. Finally, development may be carried out using as the developer an aqueous alkali solution, such as 0.1 to 5%, and preferably 2 to 3%, tetramethylammonium hydroxide (TMAH), this being done by a conventional method such as dipping, puddling, or spraying for a period of 10 seconds to 3 minutes, and preferably 30 seconds to 2 minutes. These steps result in the formation of the desired pattern on the substrate. Of the various types of high-energy radiation that may be used, the resist composition of the invention is best suited to micro-pattern formation with, in particular, deep-UV rays having a wavelength of 254 to 120 nm, an excimer laser, especially ArF excimer laser (193 nm), F₂ excimer laser (157 nm), Kr₂ excimer laser (146 nm), KrAr excimer laser (134 nm) or Ar₂ excimer laser (121 nm), x-rays, or an electron beam. The desired pattern may not be obtainable outside the upper and lower limits of the above range.

The resist composition comprising a copolymer of an acrylate monomer containing fluorine at α-position with a fluorinated hydroxystyrene derivative as a base resin according to the invention is sensitive to high-energy radiation, and has excellent sensitivity at a wavelength of up to 200 nm, especially up to 170 nm, significantly improved transmittance as well as satisfactory resolution, substrate adhesion and plasma etching resistance. These features of the inventive resist composition enable its use particularly as a resist having a low absorption at the exposure wavelength of a F₂ excimer laser, and permit a finely defined pattern having sidewalls perpendicular to the substrate to be easily be formed, making the resist ideal as a micropatterning material in VLSI fabrication.

EXAMPLE

Examples of the invention are given below by way of illustration and not by way of limitation. The abbreviations used herein are AIBN for azobisisobutyro-nitrile, GPC for gel permeation chromatography, NMR for nuclear magnetic resonance, Mw for weight average molecular weight, and Mn for number average molecular weight.

Synthesis Example 1 Copolymerization of tert-butyl α-trifluoromethylacrylate and 1.5-bis(trifluoromethyl)-p-hydroxystyrene (40/60)

In a 1-liter flask, 6.76 g of tert-butyl α-trifluoromethylacrylate and 13.24 g of 1,5-bis(trifluoro-methyl)-p-hydroxystyrene were dissolved in 300 ml of toluene. The system was fully purged of oxygen, charged with 0.42 g of the initiator AIBN, and heated at 60° C. at which polymerization reaction took place for 24 hours.

The polymer thus obtained was worked up by pouring the reaction mixture into isopropanol whereupon the polymer precipitated. The polymer collected was dissolved in tetrahydrofuran and poured into isopropanol for precipitation. This cycle was repeated twice. The polymer was separated and dried. There was obtained 12.5 g of a white polymer, which was found to have a Mw of 7,500 as measured by the light scattering method, and a dispersity (Mw/Mn) of 1.8 as determined from the GPC elution curve. On ¹H-NMR analysis, the polymer was found to consist of tert-butyl α-trifluoromethylacrylate and 1,5-bis(trifluoro-methyl)-p-hydroxystyrene in a ratio of 39:61.

Synthesis Example 2 Copolymerization of tert-butyl α-trifluoromethylacrylate. 1,5-bis(trifluoromethyl)-p-hydroxystyrene and Monomer 1 (40/40/20)

In a 1-liter flask, 6.68 g of tert-butyl α-trifluoromethylacrylate, 8.72 g of 1,5-bis(trifluoro-methyl)-p-hydroxystyrene and 4.60 g of Monomer 1, shown below, were dissolved in 300 ml of toluene. The system was fully purged of oxygen, charged with 0.42 g of the initiator AIBN, and heated at 60° C. at which polymerization reaction took place for 24 hours.

The polymer thus obtained was worked up by pouring the reaction mixture into isopropanol whereupon the polymer precipitated. The polymer collected was dissolved in tetrahydrofuran and poured into isopropanol for precipitation. This cycle was repeated twice. The polymer was separated and dried. There was obtained 11.2 g of a white polymer, which was found to have a Mw of 6,800 as measured by the light scattering method, and a dispersity (Mw/Mn) of 1.7 as determined from the GPC elution curve. On ¹H-NMR analysis, the polymer was found to consist of tert-butyl α-trifluoromethylacrylate, 1,5-bis(trifluoromethyl)-p-hydroxystyrene and Monomer 1 in a ratio of 39:41:20.

Synthesis Example 3 Copolymerization of tert-butyl α-trifluoromethylacrylate. 1,5-bis(trifluoromethyl)-p-hydroxystyrene and 3,5-bis(trifluoromethyl)styrene (40/50/10)

In a 1-liter flask, 6.81 g of tert-butyl α-trifluoromethylacrylate, 11.11 g of 1,5-bis(trifluoro-methyl)-p-hydroxystyrene and 2.08 g of 3,5-bis(trifluoro-methyl)styrene were dissolved in 300 ml of toluene. The system was fully purged of oxygen, charged with 0.43 g of the initiator AIBN, and heated at 60° C. at which polymerization reaction took place for 24 hours.

The polymer thus obtained was worked up by pouring the reaction mixture into isopropanol whereupon the polymer precipitated. The polymer collected was dissolved in tetrahydrofuran and poured into isopropanol for precipitation. This cycle was repeated twice. The polymer was separated and dried. There was obtained 13.2 g of a white polymer, which was found to have a Mw of 7,300 as measured by the light scattering method, and a dispersity (Mw/Mn) of 1.8 as determined from the GPC elution curve. On ¹H-NMR analysis, the polymer was found to consist of tert-butyl α-trifluoromethylacrylate, 1,5-bis(trifluoro-methyl)-p-hydroxystyrene and 3,5-bis(trifluoromethyl)styrene in a ratio of 39:50:11.

Evaluation

Polymer Transmittance Measurement

The polymers obtained in Synthesis Examples 1 to 3, designated Polymers 1 to 3, respectively, were determined for transmittance. Three other polymers were furnished for comparison purposes. Comparative Polymer 1 is a monodisperse polyhydroxystyrene having a molecular weight of 10,000 and a dispersity (Mw/Mn) of 1.10 in which 30% of hydroxyl groups are replaced by tetrahydropyranyl groups. Similarly, Comparative Polymer 2 is polymethyl methacrylate having a molecular weight of 15,000 and a dispersity (Mw/Mn) of 1.7; and Comparative Polymer 3 is a novolac polymer having a meta/para ratio of 40/60, a molecular weight of 9,000 and a dispersity (Mw/Mn) of 2.5.

Each polymer, 1 g, was thoroughly dissolved in 20 g of propylene glycol monomethyl ether acetate (PGMEA), and passed through a 0.2-μm filter, obtaining a polymer solution. The polymer solution was spin coated onto a MgF₂ substrate and baked on a hot plate at 100° C. for 90 seconds, forming a polymer film of 100 nm thick on the substrate. Using a vacuum ultraviolet spectrometer (VUV-200S by Nihon Bunko K.K.), the polymer layer was measured for transmittance at 248 nm, 193 nm and 157 nm. The results are shown in Table 1.

TABLE 1 Transmittance (%) 248 nm 193 nm 157 nm Polymer 1 92 9 51 Polymer 2 93 10 53 Polymer 3 93 10 54 Comparative Polymer 1 90 5 15 Comparative Polymer 2 91 80 12 Comparative Polymer 3 82 6 17

Resist Preparation and Exposure

Resist solutions were prepared in a conventional manner by formulating the polymer, photoacid generator (PAG1 or PAG2), basic compound, dissolution inhibitor (DRI1) and solvent in the amounts shown in Table 2.

-   TBA: tributylamine -   TEA: triethanolamine -   PGMEA: propylene glycol monomethyl ether acetate

On silicon wafers having a film of DUV-30 (Brewer Science) coated to a thickness of 55 nm, the resist solutions were spin coated, then baked on a hot plate at 100° C. for 90 seconds to give resist films having a thickness of 200 nm.

The resist films were exposed by means of an F₂ excimer laser (VUVES-4500 Lithotec Japan Co., Ltd.) while varying the exposure dose. Immediately after exposure, the resist films were baked at 120° C. for 90 seconds and then developed for 60 seconds with a 2.38% aqueous solution of tetramethylammonium hydroxide. The film thickness was measured in different dose areas. From the residual film thickness-to-dose relationship, the sensitivity (Eth) giving a film thickness 0 was determined. A γ value which was the slope (tanθ) of the characteristic curve was also determined.

TABLE 2 Disso- lution Photoacid Basic inhib- Eth, Polymer generator compound itor Solvent mJ/ (pbw) (pbw) (pbw) (pbw) (pbw) cm² γ Polymer 1 PAG1 TBA — PGMEA 15 20 (100) (2) (0.1) (1,000) Polymer 2 PAG1 TBA — PGMEA 12 15 (100) (2) (0.1) (1,000) Polymer 3 PAG1 TBA — PGMEA 13 16 (100) (2) (0.1) (1,000) Polymer 1 PAG1 TEA — PGMEA 18 22 (100) (2) (0.1) (1,000) Polymer 1 PAG1 TMMEA — PGMEA 16 25 (100) (2) (1,000) Polymer 1 PAG1 AAA — PGMEA 18 26 (100) (2) (1,000) Polymer 1 PAG1 AACN — PGMEA 21 35 (100) (2) (1,000) Polymer 1 PAG1 TBA DRI 1 PGMEA 13 18 (100) (2) (0.1) (10) (1,000) Polymer 1 PAG2 TBA — PGMEA 11 22 (100) (2) (0.1) (1,000) Compar- PAG1 TEA — PGMEA 18 16 ative (2) (0.1) (1,000) Polymer 1 (100)

As is evident from Tables 1 and 2, resist compositions using polymers within the scope of the invention have a high transparency at the wavelength (157 nm) of the F₂ excimer laser. It was also confirmed that upon exposure to VUV, these resist compositions exerted the positive working effect that the film thickness decreased with an increasing exposure dose.

Japanese Patent Application No. 2001-190647 is incorporated herein by reference.

Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims. 

1. A polymer comprising recurring units of the following general formulae (1a), (1b) and (1c) and having a weight average molecular weight of 1,000 to 500,000,

wherein R¹, R², R⁵ to R⁷ and R¹⁰ to R¹² each are hydrogen, a fluorine atom or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, R³ is a fluorine atom or a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms, R⁴ and R⁸ each are hydrogen or an acid labile group, R⁹ and R¹⁴ each are a fluorine atom or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, R¹³ is —C(CF₃)₂—O—R¹⁵, R¹⁵ is hydrogen or an acid labile group, a, b and c are numbers in the range: 0<a<1, 0<b<1, 0<c<1, and 0<a+b+c≦1, d is an integer of 1 to 4, e is the integer 1 or 2, and f is an integer of 0 to 4, and 1≦e+f≦5.
 2. The polymer of claim 1 wherein R³ in formula (1a) is a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms.
 3. The polymer of claim 2 wherein R³ is trifluoromethyl.
 4. A resist composition comprising the polymer of claim
 1. 5. A process for forming a resist pattern comprising the steps of: applying the resist composition of claim 4 onto a substrate to form a coating, heat treating the coating and then exposing it to high-energy radiation in a wavelength band of 100 to 180 nm or 1 to 30 nm through a photo mask, and optionally heat treating the exposed coating and developing it with a developer.
 6. The pattern forming process of claim 5 wherein the high-energy radiation is an F₂ laser beam, Ar₂ laser beam or soft x-ray.
 7. A chemically amplified positive resist composition comprising (A) the polymer of claim 1, (B) an organic solvent, and (C) a photoacid generator.
 8. The resist composition of claim 7 further comprising (D) a basic compound.
 9. The resist composition of claim 7 further comprising (E) a dissolution inhibitor.
 10. The polymer of claim 1, wherein at least one of R⁴, R⁸ and R¹⁵ is an acid labile group.
 11. The polymer of claim 1, wherein the acid labile group(s) are selected from groups of the following formulae (2) to (4):

wherein R¹⁷ is a tertiary alkyl group of 4 to 20 carbon atoms, h is an integer of 0 to 10, R¹⁸ and R¹⁹ are hydrogen or straight, branched or cyclic alkyl groups of 1 to 18 carbon atoms, R²⁰ is a monovalent hydrocarbon group of 1 to 20 carbon atoms which optionally contains a hetero atom such as oxygen, and in which optionally is substituted by hydroxyl, alkoxy, oxo, amino or alkylamino groups, furthermore, a pair of R¹⁸ and R¹⁹, a pair of R¹⁸ and R²⁰, or a pair of R¹⁹ and R²⁰, taken together, may form a ring wherein the pair is a straight or branched alkylene group of 1 to 18 carbon atoms, which optionally contains a hetero atom, R²¹ to R²³ each are a straight, branched or cyclic alkyl group of 1 to 18 carbon atoms, or a pair of R²¹ and R²², R²¹ and R²³, or R²² and R²³, taken together, may form a ring wherein the pair is a straight or branched alkylene group of 1 to 18 carbon atoms.
 12. The polymer of claim 1, wherein a to c further satisfy the range: 0.1≦a/(a+b+c)≦0.7.
 13. The polymer of claim 1, wherein a to c further satisfy the range: 0.2≦a/(a+b+c)≦0.6.
 14. The polymer of claim 1, wherein the polymer further comprises at least one copolymerized unit of one of the following formulae:

wherein, R⁰ is a straight, branched or cyclic alkyl group of 1 to 10 carbon atoms.
 15. The polymer of claim 1, wherein the polymer has a weight average molecular weight of about 2,000 to about 100,000. 